acme: include order problem in OrderError

If client.WaitOrder or client.CreateOrderCert return an acme.OrderError
it's helpful to include the order's problem field (if available). This
will often have detailed information about why a particular order
became invalid that's invaluable for debugging (e.g. a challenge
response was incorrect, a name couldn't be resolved, etc).

While it's possible for a consumer to poll the order themselves as part
of handling the order to extract a fresh Order.Error field value, it
would take an extra round-trip network request. Since we have the
underlying error in-hand when we produce the OrderError we might as well
include it directly.

Since this field is a structured object with a number of sub-fields the
OrderError.Error() function isn't updated to include the order problem
error in the String description. Interested callers should instead use
errors.Is to extract the problem information directly.

Resolves golang/go#74430

Cq-Include-Trybots: luci.golang.try:x_crypto-gotip-linux-amd64-longtest
Change-Id: I3158f064793bbfdc292dd6b5e1a6bfd7729bd980
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/681037
Auto-Submit: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Ian Stapleton Cordasco <graffatcolmingov@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

acme/types.go

@@ -154,13 +154,16 @@ func (a *AuthorizationError) Error() string {
 
 // OrderError is returned from Client's order related methods.
 // It indicates the order is unusable and the clients should start over with
-// AuthorizeOrder.
+// AuthorizeOrder. A Problem description may be provided with details on
+// what caused the order to become unusable.
 //
 // The clients can still fetch the order object from CA using GetOrder
 // to inspect its state.
 type OrderError struct {
 	OrderURL string
 	Status   string
+	// Problem is the error that occurred while processing the order.
+	Problem *Error
 }
 
 func (oe *OrderError) Error() string {